新冠疫情严控期间南京市空气质量

为研究2020年初新冠疫情严控措施对南京市空气质量的影响，选取1月25日~2月10日（疫情严控期）南京及周边省会城市空气质量监测数据，与5a同期数据进行对比，分析时空分布特征.结果表明，疫情停工期间，降水量同比下降，大气扩散条件为近5a较差水平，但除O₃浓度不降反升外，其他主要污染物PM_2.5、PM₁₀、SO₂、NO₂和CO浓度均达近5a最低值，分别为36，44，5，22μg/m³和1.1mg/m³.通过推算疫情停工期间本地减排措施的“净环境效益”，严控使得PM_2.5、PM₁₀、SO₂、NO₂和CO分别下降了41.7%、45.3%、14.3%、43.5%、18.2%，O₃浓度上升了4.8%.从空间上分析，南京市SO₂浓度及其同比降幅在长三角省会城市内排名第1，其他污染物改善情况处于中等水平.从日变化可知，PM_2.5和PM₁₀日变化由双峰型变为单峰型，夜间未出现次峰值.O₃夜间浓度明显升高，原因是交通源的大幅削减使NO对O₃的滴定反应降低，而白天O₃浓度峰值取决于VOCs和NO_x的减排比例.

Air quality in Nanjing during COVID-19 lockdown period

In order to investigate the impact of COVID-19lockdown on air quality in Nanjing, the air pollutants observed from January 25 to February 10, in 2020 (COVID-19lockdown period) in Nanjing and its surrounding cities was analyzed. During the lockdown period with poor atmospheric diffusion conditions, the concentrations of PM_2.5, PM₁₀, NO₂, SO₂, and CO decreased obviously, with the value of 36, 44, 5, 22μg/m³ and 1.1mg/m³, whereas O₃ increased by 4%. The net effectiveness of the emission reduction measures was calculated through comparisons of concentrations of air pollutants between and before COVID in the similar meteorological conditions. Concentrations of PM_2.5, PM₁₀, SO₂, NO₂ and CO decreased by 41.7%, 45.3%, 14.3%, 43.5% and 18.2%, respectively, whereas O₃ increased by 4.8%. Compared to capital cities of the Yangtze River Delta in the same period, the largest decline of SO₂ and the medium decline of the other pollutions were appeared in Nanjing. The diurnal variation concentration of PM_2.5 and PM₁₀ changed from double peak to single peak, due to the disappearance of nighttime sub-peak of particle. The concentration of O₃ increased significantly at night, which was resulted from that sharp reduction of traffic sources weaken the titration reaction of NO to O₃. The peak of O₃ during the daytime depended on the variation of the ratio of VOCs to NOx due to the emission control.